Liquid fabric treatment compositions suitable for fabric softening and static control during the laundry process are well known in the art and widespread in commercial success. These liquid fabric treatment compositions typically contain quaternary ammonium cationic surfactants (commonly referred to as quats, or quaternary fabric softeners) that provide fabric-softening and anti-static benefit during the laundry rinse cycle.
Viscosities are important in formulating both concentrated/premium liquid fabric softeners having high levels of quaternary fabric softener and dilute/discount products having low levels of actives. For concentrated products, electrolytes such as calcium chloride have been used to control viscosity, however addition of up to about 2000 ppm CaCl2 does nothing more than allow a few more percent active quaternary to be added to the formula. This is exemplified in U.S. Pat. No. 3,681,241 (Rudy at al.) wherein formulations comprising only up to about 12% active quaternary are possible. This is also exemplified in U.S. Pat. No. 4,772,404 (Fox et al.) where formulas having up to 15% quaternary blend (Varisoft 222LM and Adogen 442 in a critical ratio) are stabilized with triethanolammonium citrate and 0.09% calcium chloride. Another approach has been to combine fabric “softener” and fabric “substantive” agents. For example U.S. Pat. No. 4,155,855 (Goffinet, et al.), U.S. Pat. No. 4,157,307 (Jaeger et al.) and U.S. Pat. No. 4,855,072 (Trinh et al), describe combination of fabric softening and fabric substantive agents, wherein the fabric substantive agent is a quaternary imidazolinium salt. However, even though the compositions may contain as much as 25-50% of a blend of these two quaternary materials, only the softening agent (a conventional quaternary) appears to confer the softening and antistatic benefit to the fabric.
Other methods to stabilize concentrated fabric softener compositions having high levels of quaternary actives utilize additional surfactants, solvents or polymers. For example, as described in U.S. Pat. No. 4,326,965 (Lips et al.), stable formulas with up to 40% active quaternary are possible when incorporating 4-25% polymer having MW greater than 400. U.S. Pat. No. 4,556,502 (Blackmore et al.) describes concentrated fabric softener formulations with up to 40% active quaternary if stabilized with greater than 0.5% amphoteric surfactants and 5-30% alkanol solvent. Lastly, U.S. Pat. No. 4,233,164 (Davis) describes stabilization of 2-11% quaternary active formulations through the use of 1-5% nonionic surfactant.
Cost-reduced liquid fabric softeners may comprise lower levels of quaternary surfactant, for example less than about 10 wt. % actives and even less than about 5 wt. % actives. However, these liquids often lack any viscosity and may appear “cheap” to the consumer. Thickeners have been used to give a more “premium” appearance to dilute liquid fabric softeners having low quaternary surfactant active levels. However, some thickeners such as cationic gums and starches are not expected to change the performance of the product, but instead only expected to add cost. Examples of the use of cationic thickeners in fabric softeners is known and may be found in U.S. Pat. No. 6,949,500 (Salesses, et al.) and U.S. Pat. No. 6,514,931 (Grainger, et al.) and U.S. Patent Application Publication 2006/0252668 (Frankenbach, et al.).
Accordingly, additional development of liquid fabric softeners is warranted, ideally with research into thickeners that may bring other benefits to liquid fabric softeners other than viscosity control.